1. Field of the Invention
The present invention relates to a process for preparing an electrode for battery such as a lithium ion secondary battery.
2. Description of the Related Art
Lithium ion secondary batteries are composed of a positive electrode, negative electrode, an electrolyte and a separator etc. have a light weight, a large capacity and high charge-discharge performance, and are widely used in fields of mobile devices such as laptop computer and cellular phone and field of automobiles. Various studies have been done for establishing larger capacity and higher charge-discharge performance.
The rate determining factor to enlarge the capacity and to enhance the charge-discharge performance is a rate of reaction of an electrolyte with a positive electrode active material contained in the positive electrode and a negative electrode active material contained in the negative electrode. However, because a lithium ion conductivity of the electrolyte is low, it is important to make a distance between the positive electrode and the negative electrode shorter, and to increase areas of the positive and negative electrodes as large as possible, especially to enlarge contact areas of the electrolyte with the positive and negative electrode active materials.
Considering this viewpoint, for example, Patent Document 1 (JP2011-70788 A) proposes, in order to present an all-solid battery to achieve low cost, high safety, high energy density-high performance, a process for preparing an all-solid battery which includes three-dimensional electrodes containing active materials of concavo-convex structure.
Namely, in Patent Document 1 (Claim 1, etc.), there is proposed a process for preparing an all-solid battery which includes a first active material layer forming step by forming the first active material layer having a given concavo-convex pattern by applying a coating liquid containing a first active material to a substrate, after the first active material layer forming step, an electrolyte layer forming step by applying a coating liquid containing a polymer electrolyte on the integrated substrate in which the first active material layer is integrated on the surface of the substrate to form an electrolyte layer having convexity and concavity almost along with the concavo-convex pattern on the integrated substrate, and, after the electrolyte layer forming step, a second active material layer forming step by applying a coating liquid containing a second active material to the surface of the electrolyte layer to form a second active material layer having an almost flat surface on the opposite side to the side which contacts with the electrolyte layer.
In the above technique proposed in the Patent Document 1, however, in order to increase a capacity of the tree-dimensional electrode, when forming the first active material layer having concavo-convex pattern, it is necessary to form an active material layer having a pattern with a high aspect ratio, and to decrease a gap between the pattern.
Though there is an approach that a solid content of a slurry-like active material is made high, productivity becomes worse. When using a usual active material having a relatively low solid content, there are problems that the injected active material for forming neighboring convex parts causes liquid bleeding, or that the neighboring convex parts are brought into contact with each other. Therefore, any active material layer having a patter with a high aspect ratio cannot be obtained.
Considering the aforementioned problems, the object of the present invention is to provide a technique of a process for preparing an electrode for battery such as a lithium ion secondary battery being excellent in high charge-discharge performance by forming an active material layer having a high aspect ratio through simple process steps.